The present invention relates to a method for backing up and restoring data stored in storage apparatuses in computer systems.
Disk arrays are generally used as storage apparatuses in computer systems to provide high performance and a high degree of reliability. In xe2x80x9copen systemsxe2x80x9d such as work stations and personal computers (PCs), fixed-length block formats are used as the format with which to record data to external storage apparatuses such as disk storage apparatuses. Thus, fixed-length access interfaces are generally used in the interfaces between the open systems and disk array controllers. Fixed-length access interfaces are also used for the individual disk storage apparatuses within a disk array.
In general-purpose large-scale computers (hereinafter referred to as mainframes), variable-length block formats are used to record data to magnetic disk storage apparatuses. For this reason magnetic disk storage apparatuses are accessed using variable-length access interfaces, e.g., CKD (Count Key Data), that allow access to variable-length block format data. Conventionally, data in variable-length block formats has been physically recorded on disk storage apparatuses having variable-length access interfaces. However, in recent years there has been widespread use of disk arrays, formed from relatively inexpensive disk storage apparatuses used in PCs and workstations, as storage apparatuses for the recording of data using variable-length block formats.
In mainframe disk arrays, data is generally recorded to individual disk storage apparatuses using a fixed-length block format known as FBA (Fixed Block Architecture), as can be seen in xe2x80x9cMainframe ""98xe2x80x9d (Nikkei BP Corp., pp. 126-130). Disk array controllers are equipped with a conversion function that uses cache memory to convert between fixed-length block formats and variable-length block formats. Mainframes and disk controllers are connected using a variable-length access interface. Read/write requests from a mainframe are formed from a plurality of input/output commands known as CCWs (Channel Command Words). This plurality of CCWs is known as a CCW chain. CCW chains are created by the mainframe""s operating system in response to requests from applications.
Magnetic disk storage apparatuses are generally installed external to a mainframe as a disk subsystem formed from a disk controller and a disk storage apparatus. To read or write data to the disk storage apparatus, the mainframe sends the disk subsystem using a command based on a variable-length block format. The disk controller in the disk subsystem receives the command specified by the mainframe and converts the data from the variable-length block format to a fixed-length block format in order to allow access to the disk storage apparatus. This type of conversion from variable-length format to fixed-length format is described, for example, in Japanese laid-open patent publication number Hei 6-150557.
Computer centers today often include both mainframes and open systems. In such settings, there has been a need to allow easy management of disk arrays by storing the data accessed by the mainframes and the open systems together, thus centralizing the disk array. A technology that meets this need is described in page 145 or page 151 of xe2x80x9cMainframe ""98xe2x80x9d (Nikkei BP Corp.), where an open system can access mainframe data stored in a disk array equipped with both a variable-length access interface and a fixed-length access interface. For the mainframe data, variable-length/fixed-length block format conversion is performed within the disk array, and the data is stored in a disk storage apparatus using the fixed-length block format. The mainframe data stored in the disk storage apparatus is retrieved by an open-system server via the fixed-length block format interface. The data is retrieved in the same form as it is stored on the disk storage apparatus. Furthermore, by using a backup/restore option on the mainframe, a volume in the disk array for use by an open system can be read by the mainframe as a volume image and backed up. Also, the mainframe can restore the backed up data to the volume for use by the open system. Use of this feature does not require installation of special software on the mainframe or the open system. To allow the fixed-length block format data from the open-system volume to be accessed by the mainframe, the disk array controller converts the data to the variable-length block format. The backup destination can be an existing tape library apparatus, magnetic tape, disks, etc. When an open-system volume in the disk array is initialized, a volume serial number and volume information is created for the volume. The volume serial number and the volume information written to the volume during initialization is written to an area separate from the area in which the open-system data is written. Thus, the open-system data is not destroyed. Data stored in other disk storage apparatuses connected to the server connected to the disk array as well as data stored in disk storage apparatuses connected to other servers/clients on the network are backed up using backup programs or system commands on the open systems. The data is backed up in backup/restore volumes in the disk array. Volume information and volume serial numbers are created for the backup/restore volumes during initialization. Data that has been backed up to a backup/restore volume can, as described above, then be backed up to a tape library apparatus or the like using the mainframe""s backup feature.
There has also been the emergence of the use of SCSI interfaces, which are fixed-length access interfaces, as the interface for external storage apparatuses used for general-purpose data processing devices. For example, in pp. 53-54 of xe2x80x9cMainframe ""98xe2x80x9d (Nikkei BP Corp.), an internal disk storage apparatus is described where a disk storage apparatus that uses a fixed-length block format is mounted inside the case of a data processing device. A set of commands (CCW) for reading/writing data using the variable-length block format generated by the operating system is interpreted by a processor, referred to as an SAP, which converts these commands to a set of commands (SCSI commands) for reading/writing data using the fixed-length block format, and input/output operations are performed on the internal disk. In the data stored in the internal disk storage apparatus, data in the variable-length block format is embedded in fixed-length block format data. This conversion of data formats is performed by the SAP.
With the conventional technology described above, taking data from an external storage apparatus shared by open systems and mainframes and having the open system back the data up to a mainframe""s backup storage requires the data to be copied to a backup volume in the external storage apparatus shared with the mainframe. Thus, each time a backup is to be made, a backup volume must be created. This means that a single backup requires two backup operations. This requires allocation of storage capacity and backup processing.
The object of the present invention is to reduce the size of the backup volumes used in backup operations and to provide a method for performing backups that reduces the overhead involved in backup operations. In order to achieve the objects described above, the first form of the present invention is described as follows. In a computer system that includes a first computer, a second computer, a first storage apparatus storing data in a fixed-length block format used by the second computer, and a backup apparatus connected to the first computer and storing data in a variable-length block format, a backup method for backing up data stored in the first storage apparatus to the backup apparatus is provided. The first computer sends the second computer a request to read data in the fixed-length block format. In response to this request, the second computer reads the fixed-length block format data from the first storage apparatus and transfers this data to the first computer. The first computer converts the transferred fixed-length block format data into variable-length block format data. The converted variable-length block format data is stored in the backup apparatus. The second form of the present invention is described as follows. In a computer system that includes a first computer, a second computer, a storage apparatus storing data in a fixed-length block format used by the second computer, and a backup apparatus connected to said first computer and storing data in a variable-length block format, a backup method for backing up data stored in the first storage apparatus to the backup apparatus is provided. Volume information used to allow the first computer to access fixed-length block format data is stored in a region distinct from a region in which the fixed-length block format data is stored. Based on information contained in the volume information, the first computer reads the fixed-length block format data from the storage apparatus. In the first computer, the fixed-length block format data is converted to variable-length block format data. The first computer takes the data converted to the variable-length block format and stores it in the backup apparatus.